New planet 4 "engineer" theory

In Prometheus the engineer ship was on a desolate world testing a bio weapon. To test a bio weapon, what do you need? Test subjects or cattle. What did that high density area that got bombed by David look like in covenant? Confined space with  many "animals" that were locked in by gates.

At the end of Prometheus, Shaw wanted to go where the alien craft had come from. This does not mean that would lead to the engineer home world. They came from the planet that they were picking up their experiment subjects from.

thoughts?